The invention relates to the generation of localized cardiac measures.
Electrical activity of the heart generates an electrical potential on the body surface. At any given location on the body, this potential includes contributions from every region of the heart, with the contribution from a particular region being inversely proportional to the square of the distance from the region to the location on the body. Given the anatomy of the heart and chest, the potentials at most locations on the body surface represent summed electrical activity from a large region of the heart.
The body surface electrocardiogram (ECG) is a measure of electrical activity of the heart. The ECG provides a measure of the potential difference between two points on the body surface as a continuous function of time. The ECG is routinely measured using standard ECG electrodes. Commonly, ten electrodes are used, four of which are near the limbs and six of which span the chest, primarily on the left side. The signals recorded from these electrodes are processed to form a standard set of twelve ECG leads.
Each of the standard twelve ECG leads represents the difference between signals from two sensors that are located a significant distance from one another. Standard leads I, II and III represent the difference between pairs of the limb electrodes. They are referred to as bipolar leads because they represent the difference of two electrodes. Standard leads AVR, AVL, AVF and V1-V6 represent the difference between an electrode and Wilson's central terminal, a reference created by averaging three of the limb electrodes. Leads referenced to Wilson's central terminal are referred to as unipolar leads. Standard electrocardiogram leads, such as the unipolar leads, do not represent localized electrocardiogram signals.